A key consideration for implementing battery electric buses is the vehicle weight because the weight of the batteries generally makes battery electric buses heavier than an equivalent diesel bus. However, as battery technology continues to improve it is anticipated that the difference in weight between electric and diesel buses will reduce in the future. In New Zealand all vehicles which use public roads must comply with the Vehicle Dimensions and Mass Rule (VDAM): vehicle-dimensions-and-mass.
Land Transport Rule: Vehicle Dimensions and Mass (VDAM) 2016
VDAM sets maximum weight limits for all vehicles for the purpose of managing road surface degradation and ensuring safety of road users. For urban buses the maximum axle mass is shown in the table below, noting that the specialist vehicle limits are only allowed for buses which have a permit from the relevant road controlling authority:
| Type of axle set |
Mass without a permit (kg) |
Mass with a specialist vehicle permit (kg) |
|
Single large-tyred axle |
5,500 |
8,100 |
|
Twin-tyred axle in any axle set |
9,000 |
12,000 |
|
Two axles in a tandem axle set comprising:
|
14,500 14,500 |
16,000 18,000 |
|
Two twin-tyred axles:
|
14,500 15,000 |
17,000 18,000 |
† For a specialist vehicle permit the single large-tyred axle must be in a tandem axle set with a twin-tyred axle with a 55/45 load share.
Table 2: VDAM 2016 schedule 3 as of 1 May 2021
The following diagram shows the different common axle configurations for urban buses, with buses with two rear axles having higher weight limits because the extra rear axle spreads the vehicle weight across a larger area:
Single rear axle
Single rear axle.
Two rear axles
Two rear axles.
The maximum number of passengers which a bus is permitted to carry is determined by the lesser of two calculations which is:
Land Transport Rule: Passenger Service Vehicles 1999
The table below compares the typical gross vehicle weight to the weight limit for a selection of comparable diesel and electric buses of different sizes.
|
Bus type |
Single deck with one rear axle |
Single deck with two rear axles |
Double deck with one rear axle |
Double deck with two rear axles |
||||
|
Fuel |
Diesel |
Battery electric |
Diesel |
Battery electric |
Diesel |
Battery electric |
Diesel |
Battery electric |
|
Length |
11.5m |
11.4– 11.6m |
12.6– 13.5m |
12.6– 13.5m |
10.9m |
10.8m |
12.4– 13.5m |
12.5– 13.5m |
|
Number of rear axles |
1 |
1 |
2 |
2 |
1 |
1 |
2 |
2 |
|
Seats |
35 |
35 |
41–43 |
41–43 |
70 |
70 |
80–85 |
80–85 |
|
Standing passengers |
20 |
20 |
31–34 |
31–34 |
10 |
10 |
15–20 |
15–20 |
|
Total maximum passengers |
55 |
55 |
72–75 |
72–75 |
80 |
80 |
95–100 |
95–100 |
|
Unladen weight |
9,000 kg |
11,100 – 12,500 kg |
11,400 – 12,820 kg |
12,800 – 15,210 kg |
10,800 kg |
12,300 – 13,300 kg |
14,140 – 16,500 kg |
16,800 – 19,000 kg |
|
Gross vehicle weight |
13,400 kg |
15,580 – 16,900 kg |
17,480 – 18,820 kg |
18,800 – 21,280 kg |
17,200 kg |
18,700 – 19,700 kg |
22,220 – 24,500 kg |
24,480 – 27,000 kg |
|
NZ weight limit without permit |
14,500 kg |
14,500 kg |
20,000 kg |
20,000 kg |
14,500 kg |
14,500 kg |
20,000 kg |
20,000 kg |
|
NZ weight limit with permit |
20,100 kg |
20,100 kg |
26,100 kg |
26,100 kg |
20,100 kg |
20,100 kg |
26,100 kg |
26,100 kg |
Notes:
Please note that technical specifications vary between manufacturers and between bus models and therefore some buses may have specifications outside the range shown. The results show that all types of battery electric buses can fit within the New Zealand weight limits with a specialist vehicle permit being required in some instances. Battery Electric Buses which have a single rear axle or are double decker are more likely to require a specialist vehicle permit because there is a higher load placed on the axles. Some manufacturers produce single deck Battery Electric Buses which are within the standard weight limit and can therefore operate without a specialist vehicle permit. Whether a battery electric bus is above or below the weight limits depends on a number of factors including the size of bus, the number of passengers carried, the number of axles, the load share between axles, the number of batteries and the materials used for the batteries, chassis and body.
We recommend careful consideration of bus weights from a full bus network lifecycle perspective. There may be advantages to selecting lower weight buses that do not require specialist permits because they would have less restrictions in terms of where they can be used. They also may not require costly pavement upgrades or as much maintenance costs. This is because heavy weight buses, especially when fully laden, can cause rutting and potholes on surfaces that are not designed for high-stress use.
Further information related to road surface maintenance on bus routes is available here:
